Focusing on value is a great way to learn digital painting. Although it might be more helpful to try drawing from life or with the aid of reference photos to begin with.

I think you need more seperation between the figures and the midground, currently they don't read very clearly. Currently you only really have two planes: a very dark foreground, and a very light background. Try to add more stages inbetween and utilize the full range of light to dark. You can probably afford to make the sky even lighter in order to increase the conrast with the mountain.Going back to the figures; you should consider introducing a secondary light source in the foreground to draw attention to them.